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Tuesday, February 19, 2013

Dietary supplements ~ useless or useful?

There is a
general tenet in human nutrition that if one eats a healthy diet, then there is
no incremental benefit from taking additional nutrients either as fortified
food or as supplements. A healthy diet should provide all of one’s nutrient
requirements. I would go so far as to say that, among nutritionists, this is
more a doctrine than a mere tenet. In recent times, several papers have been
published which challenge this concept. A good place to start is with a major
survey of 12,000 US adults to ascertain and characterise usage of dietary
supplements[1].
In 2011, Americans spent $30 billion on dietary supplements, which, to put it
into perspective is equal to or greater than the annual GDP of Ethiopia, Jordan
or Bolivia. Some 77% of the users of dietary supplements do so through their
own choice with 23% doing so on professional advice. In general, users of
supplements are happier with their health than non-users, which suggests that
they use supplements as some sort of insurance. The vast majority of respondents
stated that they took supplements to “improve” or “maintain” health. So, are
they wasting their money? A recent
meta-analysis would say that indeed they are wasting their money where the end
point was mortality. In this study, the authors completed a meta-analysis of
dietary supplement (multi-minerals and multi-vitamins) intervention studies,
which involved a final list of 21 publications, involving 91,074 adults, with a
mean age of 62 and a mean duration of supplement use of 43 months. A total of 8,794
deaths was recorded. When the death rate of those assigned to intervention with
the supplements was compared to that of those receiving a placebo, no
statistically significant differences in death rate were seen. So, taking
dietary supplements doesn’t make you live longer. But do they make you
healthier?

Late in 2012, two
papers were published from the “Physicians’ Health Study II Randomized
Controlled Trial”. This began in 1997 with 14,641 male physicians aged 50 years
or greater entering the study. There were several treatments. One involved a
multi-vitamin supplement. Two others involved either vitamin E alone or vitamin
C alone. A final group received a placebo. After an average follow up of 11.2
years, 1,732 cases of major cardiovascular events (non-fatal serious heart
attack or stroke) were observed[2].
No statistically significant differences were observed in cardiovascular events
between treatment and placebo. So supplements wont make you live longer and
wont make your heart any healthier. However, a second paper from the same
Physicians Health Study Randomized Controlled trial did show that the overall
risk of cancer was moderately reduced in those assigned to the vitamin
supplements as opposed to those assigned to the placebo[3].
The authors conclude that: “Although the main reason to take multivitamins is
to prevent nutritional deficiencies, these data provide support for the
potential use of multivitamin supplements in the prevention of cancer in
middle-aged and older men.” What a pity these studies didn’t employ modern
genomics and metabolomics technology to look at responders and non-responders.
When will nutritional epidemiology enter the 21st century?

The issue of
vitamin supplementation was the subject of yet another recent paper, this time
with a focus on folic acid supplementation in the pre-natal period and during
pregnancy. Normally the end-point of such interventions would be neural tube
defects such as spina bifida but in this case it was autism. The study was
within the Norwegian Mother and Child Cohort study, which recorded the use of
folic acid prior to conception and in the first 8 weeks of pregnancy[4].
Among the 85,176 children born in the cohort after exclusion of some births
(12,000) for reasons such as premature delivery or lack of data on folic acid
use, some 114 cases of autism were observed, equating to a rate of 0.14%. Among
women who took folic acid supplements the rate was 0.10% while among women who
didn’t take folic acid supplements the rate was 0.21%. This difference was
statistically significant even when controlled for maternal and paternal
education and age, a planned pregnancy, parity, year of birth and maternal BMI
and smoking habits.

Clearly, some
people benefit from dietary supplement use and the challenge to nutritional
science must be to use modern technologies to ascertain those that do and don’t
benefit with a view to customizing supplement use to optimise health. The
doctrine that states that you should get all your nutrients from foodstuffs is
codswallop.

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"Ever seen a fat fox ~ Human obesity explored"

About Me

I graduated from University College Dublin in 1971 with an Masters in Agricultural Chemistry, took a PhD at Sydney University in 1976 and joined the University of Southampton Medical School as a lecturer in human nutrition in 1977. In 1984 I returned to Ireland to take up a post at the Department of Clinical Medicine Trinity College Dublin and was appointed as professor of human nutrition. In 2006 I left Trinity and moved to University College Dublin as Director of the UCD Institute of Food and Health. I am a former President of the Nutrition Society and I've served on several EU and UN committees on nutrition and Health. I have published over 350+ peer reviewed scientific papers in Public Health Nutrition and Molecular Nutrition and am principal investigator on several national and EU projects (www.ucd.ie/jingo; www.food4me.org). My popular books are "Something to chew on ~ challenging controversies in human nutrition" and "Ever seen a fat fox: human obesity explored"